1. Field
Communication systems may benefit from apparatuses and methods for providing additional capacity for local area communications over an air interface. Relevant air interfaces can include those used with radio frequency communication systems.
2. Description of the Related Art
As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become more widely deployed and continue to attract a growing number of users, it may valuable to accommodate a large and variable number of communication subsystems transmitting a growing volume of data with a fixed resource such as a fixed channel bandwidth accommodating a fixed data packet size. Traditional communication system designs employing a fixed resource, for example, a fixed data rate for each user, have become challenged to provide high, but flexible, data transmission rates in view of the rapidly growing customer base.
Conventional systems implement wireless communications using standard protocols including Universal Mobile Telecommunications System (“UMTS”), UMTS Terrestrial Radio Access Network (“UTRAN”), and third generation wireless (“3G”) now extending to advanced standards including, for example, fourth generation wireless (“4G”) and Wideband Code Division Multiple Access (“WCDMA”) which support HSDPA communications between mobile equipment. The mobile equipment includes user equipment (“UE”) such as cell phones, and fixed transceivers that support mobile telephone cells, such as base stations, referred to as “Node B” (or “NB”) and when enhanced, or evolved to a new standard protocol, referred to as “e-Node B” (or “eNB”).
The Third Generation Partnership Project Long Term Evolution (“3GPP LTE”) is a name generally used to describe an ongoing effort across the industry to improve UMTS. The improvements are being made to cope with continuing new requirements and the growing base of users. Goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards and backwards compatibility with some existing infrastructure that is compliant with earlier standards. Recently, the deployment of systems is extending to “LTE-Advanced” as additional bandwidth and features are added.
UTRAN includes multiple Radio Network Subsystems (“RNS”), each of which contains at least one Radio Network Controller (“RNC”). However, the RNC may not be present in all systems incorporating Long Term Evolution (“LTE”) of UTRAN, evolved UTRAN (“E-UTRAN”). LTE may include a centralized or decentralized entity for control information. In UTRAN operation, each RNC may be connected to multiple Node Bs which are the UMTS counterparts to Global System for Mobile Communications (“GSM”) base stations. In E-UTRAN systems, the e-Node B is, or may be, connected directly to the access gateway (“aGW,” sometimes referred to as the services gateway “sGW”). Each Node B may be in radio contact with multiple UE devices (generally, user equipment including mobile transceivers or cellular phones, although other devices such as fixed cellular phones, mobile web browsers, tablets, ebook readers, navigation systems, laptops, PDAs, MP3 players, and gaming devices with transceivers may also be a UE) via the radio air interface.
The wireless communication systems as described herein are applicable to, for instance, 3G, and UTRAN systems as well as 3GPP LTE and LTE-A compatible wireless communication systems. In general, E-UTRAN resources are conventionally assigned by the network to one or more UE devices by use of various resource allocation means, or more generally by use of a downlink resource assignment channel or physical downlink control channel (“PDCCH”). LTE is a packet-based system and, therefore, there may not be a dedicated connection reserved for communication between a UE and the network. Users are generally scheduled on a shared channel every transmission time interval (“TTI”) by a Node B or an e-Node B. A Node B or an e-Node B controls the communications between user equipment terminals in a cell served by the Node B or e-Node B. In general, one Node B or e-Node B serves each cell. Resources needed for data transfer are assigned either as one time assignments or in a persistent/semi-static way. The LTE, also referred to as 4G, generally supports a large number of users per cell with quasi-instantaneous access to radio resources in the active state.
Additional spectrum/bandwidth is being provided in various ways. In one approach to adding broadband spectrum, additional base stations for communications with user equipment are deployed. These may include so-called “femto-cells” or cells provided by “Home enhanced Node B” stations, sometimes called “HeNBs”. A HeNB may provide wireless interface to user equipment in a home, office, restaurant or other space where the users may share the resource. The user equipment devices may include cellular phones, PDAs, tablet computers, laptop computers, portable or fixed devices such as web browsers, audio players, video players and others. The area serviced by a femtocell or HeNB may be, for example, limited to 30 to 50 meters in radius. Deploying these base stations may provide users with a signal in the home or office, reducing or eliminating the need for wired telephones for example, and making it possible to rely on a cellular phone in buildings where previously, signal strength and reception were not sufficient. Additional bandwidth is also provided for the system, reducing the need for the eNB base station in the area to provide all of the wireless service. It is also envisioned that user equipment (“UE”) can act as a HeNB.
One aspect of HeNB deployment is that, in contrast to the deployment of system managed base stations, the placement of new HeNBs is uncoordinated and may be performed by users. The HeNBs may be placed in very close physical proximity, such as installed in homes adjacent one another, in offices, apartments, townhomes and the like. A particular user equipment may, therefore, often be physically closer to a neighboring HeNB than the HeNB the user device is in cellular communication with, and interference between the HeNB cells can occur.
Multiple uncoordinated deployed HeNBs may operate on the same frequency band. Some of these networks may provide services not available from other HeNBs. The HeNBs and users may utilize closed subscriber groups (“CSGs”). A user interested in using these services may be physically closer to, or in better signaling receiving condition with, an interfering HeNB, instead of the HeNB of interest.
Typically, a frequency band has multiple channels and the HeNB operates on one of these channels. To minimize interference, HeNBs capable of causing strong interference to one another are conventionally placed on different channels. There are several further approaches to minimize interference. In one distributed approach, HeNBs try to maximize the path loss to other HeNBs sharing the same frequency channel. In an alternative approach, a centralized scheme is used in which the HeNBs report measurements to a network node, and the network node then assigns the channels in a manner that will reduce interference between HeNBs.
If an HeNB could utilize carrier aggregation, then additional capacity could be accessed by an HeNB. However, carrier aggregation for HeNBs is not conventionally known. For example, Release 10 of the LTE standard does not allow carrier aggregation for HeNBs. Conventionally, the interference coordination schemes have been limited to coordinating the interference with co-channel deployments of macro-cells.
An approach to address the interference that has been previously described in “Interference Management in Local Area Environments for LTE-Advanced,” L. G. U. Garcia, K. I. Pedersen, and P. E. Mogensen, IEEE Communications Magazine, Vol. 47 (9):110-116, September 2009, which is hereby incorporated herein by reference in its entirety; as an autonomous component carrier selection scheme (“ACCS”). In this scheme, dynamic frequency reuse mechanisms are used. Each HeNB selects a subset of available component carriers in a distributed manner. The HeNBs also learn the environment using signal to interference plus noise (“SINR”) estimates provided by active user equipment. The UEs measure the downlink received signals (from HeNB to UE) as part of normal system operations and these estimates may be collected. Based on long term statistics collected, SINR values are determined for all neighboring cells which can be considered as potential interferers. The proposed ACCS scheme also has the HeNBs or the network storing the environment information, for example, in background information matrices (“BIM”) which are used later in the channel selection decision process.
In ACCS, it is proposed that each HeNB will maintain a list of potentially interfering cells. Also, the eNB measurements are aggregated into a table form; for example, an inter-cell radio resource allocation table (“RRAT”). This table contains information regarding which component carriers are allocated as primary and secondary carriers in the cells. Based on the information stored in the BIMs and the RRAT, the HeNBs do carrier selection in a distributed manner without violating the minimum SINR conditions for surrounding cells. One of the main assumptions in this scheme is the a priori knowledge of minimum target SINR values for primary and secondary carriers. These target SINR requirements can be set, for example, by a network planning tool or by the administering device such as an Operations and Maintenance tool which controls the HeNBs. ACCS is also described, for example, in a paper entitled “Autonomous Component Carrier Selection for Local Area Uncoordinated Deployment of LTE-Advanced,” L. G. U. Garcia, K. I. Pedersen, and P. E. Mogensen, IEEE Vehicular Technology Conference (VTC), Anchorage Ak., USA September 2009, which is hereby incorporated herein by reference in its entirety.
In future standards, such as future LTE-Advanced standards, it is foreseen that the use of carrier aggregation will be supported for HeNBs. Further, it is also clear that if the HeNBs are deployed with similar density as for wireless hotspots (“Wi-Fi” access points) then some interference management between deployed HeNBs will be needed.
A need thus exists for systems and methods to efficiently provide carrier aggregation and interference management for local area base stations such as HeNBs for cellular communications, without the disadvantages of the known prior approaches.